From: Li Nan <[email protected]>
echo max of u64 to cost.model can cause divide by 0 error.
# echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model
divide error: 0000 [#1] PREEMPT SMP
RIP: 0010:calc_lcoefs+0x4c/0xc0
Call Trace:
<TASK>
ioc_refresh_params+0x2b3/0x4f0
ioc_cost_model_write+0x3cb/0x4c0
? _copy_from_iter+0x6d/0x6c0
? kernfs_fop_write_iter+0xfc/0x270
cgroup_file_write+0xa0/0x200
kernfs_fop_write_iter+0x17d/0x270
vfs_write+0x414/0x620
ksys_write+0x73/0x160
__x64_sys_write+0x1e/0x30
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,
overflow would happen if bps plus IOC_PAGE_SIZE is greater than
ULLONG_MAX, it can cause divide by 0 error.
Fix the problem by setting basecost
Signed-off-by: Li Nan <[email protected]>
Signed-off-by: Yu Kuai <[email protected]>
---
block/blk-iocost.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index f8726e20da20..c6b39024117b 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -866,9 +866,13 @@ static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
*page = *seqio = *randio = 0;
- if (bps)
- *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
- DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
+ if (bps) {
+ if (bps >= U64_MAX - IOC_PAGE_SIZE)
+ *page = 1;
+ else
+ *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
+ DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
+ }
if (seqiops) {
v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);
--
2.31.1
On Mon, Dec 26, 2022 at 04:58:58PM +0800, Yu Kuai wrote:
> From: Li Nan <[email protected]>
>
> echo max of u64 to cost.model can cause divide by 0 error.
>
> # echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model
>
> divide error: 0000 [#1] PREEMPT SMP
> RIP: 0010:calc_lcoefs+0x4c/0xc0
> Call Trace:
> <TASK>
> ioc_refresh_params+0x2b3/0x4f0
> ioc_cost_model_write+0x3cb/0x4c0
> ? _copy_from_iter+0x6d/0x6c0
> ? kernfs_fop_write_iter+0xfc/0x270
> cgroup_file_write+0xa0/0x200
> kernfs_fop_write_iter+0x17d/0x270
> vfs_write+0x414/0x620
> ksys_write+0x73/0x160
> __x64_sys_write+0x1e/0x30
> do_syscall_64+0x35/0x80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,
> overflow would happen if bps plus IOC_PAGE_SIZE is greater than
> ULLONG_MAX, it can cause divide by 0 error.
>
> Fix the problem by setting basecost
>
> Signed-off-by: Li Nan <[email protected]>
> Signed-off-by: Yu Kuai <[email protected]>
> ---
> block/blk-iocost.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index f8726e20da20..c6b39024117b 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -866,9 +866,13 @@ static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
>
> *page = *seqio = *randio = 0;
>
> - if (bps)
> - *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
> - DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
> + if (bps) {
> + if (bps >= U64_MAX - IOC_PAGE_SIZE)
> + *page = 1;
> + else
> + *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
> + DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
> + }
This is a nitpick but wouldn't something like the following be easier to
understand?
if (bps) {
u64 bps_pages = DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE);
if (bps_pages)
*pages = DIV64_U64_ROUND_UP(VTIME_PER_SEC, bps_pages);
else
*pages = 1;
}
Out of scope but this seems more like a bug in the DIV macros. The fact that
it returns 0 is an implementation artifact more than anything and a
surprising one at that as it ends up returning 0 for an input that a regular
division would handle just fine and the rounded up result fits well within
the result type.
Thanks.
--
tejun
Hi,
?? 2023/01/05 5:54, Tejun Heo ะด??:
> On Mon, Dec 26, 2022 at 04:58:58PM +0800, Yu Kuai wrote:
>> From: Li Nan <[email protected]>
>>
>> echo max of u64 to cost.model can cause divide by 0 error.
>>
>> # echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model
>>
>> divide error: 0000 [#1] PREEMPT SMP
>> RIP: 0010:calc_lcoefs+0x4c/0xc0
>> Call Trace:
>> <TASK>
>> ioc_refresh_params+0x2b3/0x4f0
>> ioc_cost_model_write+0x3cb/0x4c0
>> ? _copy_from_iter+0x6d/0x6c0
>> ? kernfs_fop_write_iter+0xfc/0x270
>> cgroup_file_write+0xa0/0x200
>> kernfs_fop_write_iter+0x17d/0x270
>> vfs_write+0x414/0x620
>> ksys_write+0x73/0x160
>> __x64_sys_write+0x1e/0x30
>> do_syscall_64+0x35/0x80
>> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,
>> overflow would happen if bps plus IOC_PAGE_SIZE is greater than
>> ULLONG_MAX, it can cause divide by 0 error.
>>
>> Fix the problem by setting basecost
>>
>> Signed-off-by: Li Nan <[email protected]>
>> Signed-off-by: Yu Kuai <[email protected]>
>> ---
>> block/blk-iocost.c | 10 +++++++---
>> 1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
>> index f8726e20da20..c6b39024117b 100644
>> --- a/block/blk-iocost.c
>> +++ b/block/blk-iocost.c
>> @@ -866,9 +866,13 @@ static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,
>>
>> *page = *seqio = *randio = 0;
>>
>> - if (bps)
>> - *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
>> - DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
>> + if (bps) {
>> + if (bps >= U64_MAX - IOC_PAGE_SIZE)
>> + *page = 1;
>> + else
>> + *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
>> + DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
>> + }
>
> This is a nitpick but wouldn't something like the following be easier to
> understand?
>
> if (bps) {
> u64 bps_pages = DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE);
>
> if (bps_pages)
> *pages = DIV64_U64_ROUND_UP(VTIME_PER_SEC, bps_pages);
> else
> *pages = 1;
> }
>
Yes, I agree that this is better to understand. I'll send a new version.
Thanks,
Kuai